1. Field of the Invention
The invention relates to a complete knee prosthetic, the type of which includes a tibia part comprising a support plate which is horizontal and fastened by means of appropriate anchoring means to the tibia which has been re-sectioned. It also includes a meniscus, which is generally in a plastic material and is put down on the tibia plate so as to be fastened or removable, and a femoral part which includes one or two condyles on the one side and a trochlea part on the other side. The present invention also relates to a femoral part of such a prosthetic.
2. Description of the Related Art
The external surface of the one or many condyles of the femoral part is generally spherical. When observed from a sagittal perspective, i.e. a perspective parallel to the axis of the tibia and/or to the axis of the femur when the knee is bent and thus also parallel to the pre-posterior axis, the shape of the condyles is an arc, the angle of which extends over the normal flexing range of a knee, i.e. zero to one hundred and twenty or one hundred and thirty degrees. The spherical surface of the condyle co-operates with the corresponding upper surface of the meniscus, which has a shape that is complementary to the spherical shape of the condyles, by means of a sliding action.
A prosthetic of this type is known, for instance from international patent application WO92/03108 of British Technology Group. The disadvantage of this type of prosthetic according to the prior art is that it is preferable to implement this prosthetic with conserving the posterior crossed ligament (PCL). In complete knee prosthetics according to the prior art, the femoral part can slide beyond zero degrees, i.e. beyond the vertical position defined by the tibia and the femur being parallel and thus into the range of negative angles of rotation. Said negative angles correspond to the fact that the tibia abnormally closes in on the femur from the front of the leg, as opposed to normally closing in on the femur from the back of the leg when one flexes the knees. This situation may eventually result in the dislocation of the meniscus or the femoral part, in the case of an implementation without conserving the posterior crossed ligament.
A complete prosthetic of this type is also known from European Patent 0 653 927 in the name of Walker, granted from PCT application WO94/26212. A cavity is implemented in the condyle to enable a perfect congruence when a flexing angle is null (knee extended). It is also preferable for this prosthetic to be implemented with conserving the posterior crossed ligament, for the same reasons as previously explained.
According to the invention, the above disadvantages are overcome by providing a complete knee prosthetic which can be implemented either with or without the posterior crossed ligament, and notably without the posterior crossed ligament, without said negative angles of rotation being permitted to reach values beyond minus five or minus ten degrees.
A complete prosthetic of the knee according to the invention includes a femoral part and a meniscus, with said femoral part comprising at least one condyle and a trochlea part, wherein said one or a plurality of condyles each have an external surface, the shape of which complements the respective upper surface of said meniscus in order to obtain a congruence of said surfaces on at least part of the normal flexing range. At least one cavity and the relative emplacements are implemented in said trochlea part, the dimensions and shapes of said at least one cavity and the anterior upper edge of said meniscus being such that the femoral part is blocked in its flexion by rotation in the case of negative angles beyond an inferior negative angle limit.
A cavity is implemented in the trochlea part of the femoral part, which can rest on the anterior side against part of the upper edge of the meniscus according to a flexing angle of for instance of minus five degrees. The femoral part thus comes to rest against the abutment which is the meniscus by means of the cavity implemented in the trochlea and therefore cannot follow its rotation through to negative angles. Consequently, the complete knee prosthetic cannot flex in the wrong direction even though the posterior crossed ligament is not present. According to the prior art, it is indeed said posterior crossed ligament which prevents this rotation into negative angles. According to the invention, even if the posterior crossed ligament is not present anymore, this rotation into negative angles is prevented.
According to a preferred embodiment of the present invention, the value of said inferior negative angle limit is comprised between zero and minus ten degrees, preferably equal to minus five degrees.
According to a preferred embodiment of the present invention, said upper edge includes at least one shaped projection, in a sagittal perspective, complementary with said one or more of cavities such that said one or more projections come to rest against said one or more cavities.
According to a preferred embodiment of the present invention, said one or more projections have a height superior to the height of the posterior upper edges, relative to the flat base of the meniscus.
According to a preferred embodiment of the present invention, said one or more condyles are spherical in shape.
According to a preferred embodiment of the present invention, said condyles comprise two circular segments in a sagittal perspective, with the first of said segments being an intermediary circular segment with a greater radius and the second of said segments being an extremity circular segment with a smaller radius.
According to a preferred embodiment of the present invention, the cavity is implemented in the trochlea part at the level corresponding to an angle of ten to thirty degrees along the circular segment corresponding to the projection of the trochlea part in a sagiftal perspective, from the end of said condyles.